G-protein coupled receptors are cell surface receptors that indirectly transduce extracellular signals to downstream effectors, e.g., intracellular signaling proteins, enzymes, or channels. Changes in the activity of these effectors then mediate subsequent cellular events. The interaction between the receptor and the downstream effector is mediated by a G-protein, a heterotrimeric protein that binds GTP. Examples of mammalian G proteins include Gi, Go, Gq, Gs, and Gt.
G-protein coupled receptors (“GPCRs”) typically have seven transmembrane regions, along with an extracellular domain and a cytoplasmic tail at the C-terminus. These receptors form a large superfamily of related receptor molecules that play a key role in many signaling processes, such as sensory and hormonal signal transduction. The further identification of GPCRs and the natural ligands of the receptors is important for understanding the normal process of signal transduction and as well as its involvement in pathologic processes. For example, GPCRs can be used for disease diagnosis as well as for drug discovery. GPCR ligands may be used for the treatment of GPCR-related disorders and for the identification of additional modulators of GPCR activity. Further identification of GPCRs and ligands that bind to GPCRs is therefore of great interest.